Lifepo4 house / lead starting bank interaction?

[Iggy]

This the way I set up my LifePo4 house batteries. 3 years ago. I would say get as many charging amps as you can to start. I have added more batteries since the original. I also added an A/C charger (60 amp) from gen set to batteries.

One thing, but that's me. Can the ALT from the genset handle the load. I did the same thing, but installed a breaker only for being on the hard in the winter time. That ALT was only sizes to handle it's battery.

 

[Portage_Bay]

I have twin 210hp cummins 6bt's. What is the minimum reasonable start battery size i can install?

Not sure what you're trying to accomplish, why you would want to skimp on starting bank. Loosing your house bank is annoying. Loosing ability to start the engines is another thing entirely. Here's a link to a reliable source on starting battery size for the Cummins 6BT
https://tadiesels.com/img/cummins/docs/cummins-6BTA59-370_general-data.pdf
where I find

A good group 31 starting battery may meet those specs. What you might consider is one start battery for both mains and upping the size of your generator start battery to match. This would give you some reduncancy. While a separate start battery for each engine is ideal my last boat had one start battery shared by a pair of CAT 3208s. It was a space problem and worked well.

 

[Delfin]

For those with a lithium house bank, how are you getting the alternator charge to your house? And then conversely, how are you keeping your lead start batts charged if you are not moving around regularly? Is two "dc to dc" chargers (one for each direction) the standard solution? Or is there a better way?

I need to switch my house bank from GC2's to Lifepo4. I'm disapointed to see how much other stuff i'm going to need to add/replace in the process.

If you have a 1, 2, Both switch to select the start or house banks you have everything you need. Keep the charge sources directed to Start LA when underway, or if House LFP needs charging, select that bank as the destination. It's what I been doing for many years through thousands of miles of cruising and I remain perplexed why a simple problem that most boats already have a solution in place for is "solved" with more complex, expensive and unnecessary alternate solutions. But to each his own.

 

[SteveK]

If you have a 1, 2, Both switch to select the start or house banks you have everything you need. Keep the charge sources directed to Start LA when underway, or if House LFP needs charging, select that bank as the destination. It's what I been doing for many years through thousands of miles of cruising and I remain perplexed why a simple problem that most boats already have a solution in place for is "solved" with more complex, expensive and unnecessary alternate solutions. But to each his own.

I wish more like you would speak up as the scare of doing what you do is now ingrained and avoided therefore we do not know what would happen if we followed your method.
Oh there were quite a few that burned up the ALT, was reason enough for me.

 

[Iggy]

If you have a 1, 2, Both switch to select the start or house banks you have everything you need. Keep the charge sources directed to Start LA when underway, or if House LFP needs charging, select that bank as the destination. It's what I been doing for many years through thousands of miles of cruising and I remain perplexed why a simple problem that most boats already have a solution in place for is "solved" with more complex, expensive and unnecessary alternate solutions. But to each his own.

Generally speaking, You can not charge AGM and Lifo4 with the same charging parameters. They should be using separate sources set for each type of batteries. The only way both would need the same bulk, float, abortion voltages and more.

You run the risk of fire, or just ruining your batteries.

 

[J.T kearney]

Wow this thread really took off without me. I'm different than most you guys in that my boat moves very infrequently, but spends its entire life at anchor. I have 1700w of solar. I don't need to run a generator too often but i do have a diesel, as well as a portable gas unit with a built in battery + pull cord. I have twin 6bt engines, no idea on the alternators, obviously not very consequential with this much solar and so little engine time.

I have a mini dc aircon that i run at about 180 watts at night in the summer (crank it up to 275w if i wanna chill during the day). Have an old 12v marine "apartment sized fridge/freezer" that runs continuous (unless its winter), as well as a regular 120v 5cu ft chest freezer. Add in a few fans, and i'm basically pulling 20-30amps (12v) continuous overnight in the summer.

I put in 1075ah duracell gc2's 3 years ago, but it doesn't look like they can do another summer. I currently have no dedicated start batteries, i wanted the biggest house bank i could fit. So as you can see several things need to change to accomodate a lifepo4 house, but i obviously need lithium.

Not sure if I could keep 4 of the gc2's for starting. They're not made for it and are probably beat, but at the very least I would want a way to keep them topped.

I also have an antique (apparently installed in 2003!) xantrex freedom 10 inverter/charger. It's been on continuously for 5 years with no issues. But can it be used to charge lithium? A guy at xantrex said no. I also have 1 old solar controller (C40 PWM), which he also said can't do lithium. But it has manual knobs for bulk and float voltages. Do I really gotta junk that too?

ERTF
check with your lifepo4 battery manufacturer for spec's . Keep asking questions until every thing is clarified. I have 4 100 amp epochs and they are able to run my bow thruster. I believe its because each battery has it's own BMS and the thruster is pretty close to being starter motor. I still have a dedicated start battery and won't leave the dock with out it.

 

[Delfin]

Generally speaking, You can not charge AGM and Lifo4 with the same charging parameters. They should be using separate sources set for each type of batteries. The only way both would need the same bulk, float, abortion voltages and more.

You run the risk of fire, or just ruining your batteries.

Since I'm on year seven of doing exactly what I described, and having just done a capacity test of the LFP bank showing 96% capacity, I have to disagree. And just FYI, but Interstate advises to keep bulk charge levels "less than 15-17 volts" for their AGM batteries, so no, there is no incompatibility between the two chemistries charging needs, other than duration of the absorption phase, which is a non issue in the software I use. Also, there's no point in even using AGM for a starter bank rather than cheaper FLA, at least none that comes to mind.

 

[Delfin]

I wish more like you would speak up as the scare of doing what you do is now ingrained and avoided therefore we do not know what would happen if we followed your method.
Oh there were quite a few that burned up the ALT, was reason enough for me.

I make the presumption that anyone installing an LFP bank also has a modern three stage smart regulator, so alternator output can be throttled to prevent overheating even the whimpiest of alternators. Mine is set to 75% capacity, and it's 18 years old and doing fine.

 

[ERTF]

Not sure what you're trying to accomplish, why you would want to skimp on starting bank.

Is it not obvious? Space on a boat is finite. I'm trying to accomplish not wasting a bunch of space on excess start batteries, so I can maximize my house bank. Seeing as I will have all this power in a house bank, it would be nice to be able to rely on that as a back up starter (as could always be done with lead). But that is sounding iffy with the bms limitations. Interestingly, on another forum the tone is totally opposite regarding charging lifepo4 and using as backup for starting.

 

[SteveK]

I make the presumption that anyone installing an LFP bank also has a modern three stage smart regulator, so alternator output can be throttled to prevent overheating even the whimpiest of alternators. Mine is set to 75% capacity, and it's 18 years old and doing fine.

Never make that assumption. With a remote REG you can charge LFP under control.

 

[rslifkin]

Also, there's no point in even using AGM for a starter bank rather than cheaper FLA, at least none that comes to mind.

It depends on the boat. AGMs get rid of the need for frequent access for watering and also greatly reduce concerns about acid spills and only vent fumes if something is wrong. So that gives more flexibility in placing the start batteries. On some boats there may be a good place for a start battery that isn't suitable for FLA, but would be fine for an AGM.

If you can use FLA for start and don't mind needing to water them periodically, it's certainly the cheaper option.

 

[Delfin]

It depends on the boat. AGMs get rid of the need for frequent access for watering and also greatly reduce concerns about acid spills and only vent fumes if something is wrong. So that gives more flexibility in placing the start batteries. On some boats there may be a good place for a start battery that isn't suitable for FLA, but would be fine for an AGM.

If you can use FLA for start and don't mind needing to water them periodically, it's certainly the cheaper option.

They do make maintenance free 8D batteries. About $285 each. You're right on the more varied footprint available for AGM batteries. I started out with Northstar AGMs because of their energy density, allowing the placement of a large house bank in a smaller space.

 

[Bmarler]

Thanks TT!
I'm looking forward to adding the dc2dc chargers. The 12v alternator and 24 house bank has been driving me nuts (not being able to send any charge to the house bank while running). This site always comes through.

Thanks ERTF for starting this thread!

Have you looked at the balmar small case 24 volt alternators? The xt series might fit? That’ll put out 90 amps at 24 volts and would be great for a lithium bank.

 

[Mac2]

Have you looked at the balmar small case 24 volt alternators? The xt series might fit? That’ll put out 90 amps at 24 volts and would be great for a lithium bank.

I am now! Thanks for the heads up. This alternator with a WS500 would be a great set-up.

 

[Greg QS]

I have twins. 1 does the lithium house bank and the other does La starter bats .
Gensets will run chargers for all different batteries.
Never checked if the bat chargers are on the inverter. Then I could charge start bats off the house bank if needed by inverting to 110 volt.

 

[Mambo42]

As others have stated, LiFePO4 and AGM do not have the same charging specifics, so cannot combine them. Lithium can be charged at full charge until it reaches the full state, after that it will start balancing. AGM first goes at full charge and nearing 90 % it will lower the charge in order to get to 100 %. So combining them on one charging spec is not going to work.
The good part of Victron is that you can maximize the amps the inverter/charger will draw from your generator. E.g. if your inverter can charge at 200 A maximum you can set it at a lower rate so you will have amps available for cooking, washing etc. If your generator would be able to charge less than what the inverter/charger can accept and you don't lower the charging amps the fuse on your generator will simply blow.

On my boat I have basically 3 different battery banks:
1. Service bank, which is 24 V at 1400 Ah
2. Start battery bank which is 12 V (4 x 75 Ah)
3. Bow and stern thruster plus windlass and that is 24 V (at 150 Ah) again.

The service bank can be charged in 4 different ways. That can be via generator or shore power (via the inverter/charger), the solar panels or via the 24 V alternators on the engines which are regulated using wakespeed. While on anchor the solar panels have more than enough capacity (3 Kwp) to charge the service bank in about 4 to 5 hours after a one night use. Even when there is not enough sun I can go 3 days without charging and normally we have then picked up the anchor to move to a different place during which travel the alternators will charge the house bank again.

The start batteries get charged via 12 V alternators, also on the engine, so when the engines run the start batteries get charged to 100 % again.

The third bank gets charged via a 220 V to 24 V smart battery charger that is connected to the service bank via the inverter. This means that as long as the service bank has enough juice those batteries will get charged. After all, when you come into an anchorage or port you shut down the engines and that would mean the bow thruster batteries would not get charged anymore if I would have hooked them up to an alternator.

All I can say is that I have more than enough Ah onboard to not having to use the generator anymore. I just run it every now and then for the sake of running it, but it is no longer required to charge the batteries or run any of the systems onboard. Also during night passages it is not a problem anymore. In the past I had to run the generator in order to be able to run all the required equipment, but now the 24 V alternators keep the service bank full at all times, they have a max capacity of 400 A and that is much more than required.
Also, since I upgraded from 500 Ah to 1400 Ah I don't need to start the generator for cooking or using the dishwasher or boiler anymore. On the 500 Ah AGM I basically only had 250 Ah available and that meant cooking was not possible, I would drain the batteries to below 50 % if I would take them through the night. After all, on anchor our boat systems (lights, radio, stabilizers, pumps etc) would draw about 15 A per hour, so in one night that could be around 150 - 200 Ah. The remaining 50 - 100 Ah would not be enough for cooking, tv, dish washer or washing machine. Since I changed to 1400 Ah those problems are over. Even when I use 500 Ah overnight, the solar panels can fill up the batteries in 4 to 5 hours.

In all I am very happy with the current set up and can highly recommend this path. I do admit it is a costly affair, but the pros outweigh the cons:
1. no more running the generator in quiet anchorages
2. no need to stay awake because the generator has to charge the batteries at night
3. an increased range because am not burning fuel for the generator anymore
4. generator does not increase in hours anymore, which means it will keep its value and I don't need to replace it.
5. but most important, we can use all the equipment onboard at any time and no need to plan usage of equipment anymore.

For us changing to LiFePO4 has given us much more freedom and has decreased our fuel bill by around 5.000 euro per year and increased our range with around 1200 nm. And that means we can now go from one place with low fuel to cost the next one with low fuel cost without the need of fueling in between. At a saving of 50 cents per liter that is around 1250 euro savings each time we fuel up. We fuel up 2 or 3 times a season, so that is an additional 3000 - 3500 euro savings. Total savings in one season in fuel is around 8000 euro. However, since we don't need shore power anymore the savings have gone up even more. Nowadays they charge between 2 and 3 euro per kwh in a port or marina. We would normally use between 6 and 7 Kwh per day, so each time we have to be in port we save an additional 12 to 21 euro. Not a lot, but we will take it.

 

[Delta Riverat]

I don't see a problem with a "momentary" parallel of lithium & lead. My new (soon to be) LiFePO4 house bank will do 600A continuous and 1200A for 5 seconds. Twelve hundred amps should start a diesel. Mine catch almost as soon as they turn, not more than 2 seconds.

Of course you should not leave this sharing after start, the 2 chemistries are not compatible long term charging wise. But for an emergency start I see no problem with sharing.

 

[Mambo42]

I don't see a problem with a "momentary" parallel of lithium & lead. My new (soon to be) LiFePO4 house bank will do 600A continuous and 1200A for 5 seconds. Twelve hundred amps should start a diesel. Mine catch almost as soon as they turn, not more than 2 seconds.

Of course you should not leave this sharing after start, the 2 chemistries are not compatible long term charging wise. But for an emergency start I see no problem with sharing.

In my opinion it should not be a problem to use a lithium battery bank for starting the engines, it is indeed only a short burst.
Linking start batteries and Lithium and then charging them at the same time..........that is something I would not do. Better to connect a separate charger, connect that to the lithiums and then start charging the start batteries. That way you will be safe.

 

[cafesport]

The op seems to be a good candidate for using a start cap instead of a start batt. Dave Marlow started a pair of c18's three times on one of his boats using one. Easy to recharge off the house batts too.

 

[Delfin]

As others have stated, LiFePO4 and AGM do not have the same charging specifics, so cannot combine them. Lithium can be charged at full charge until it reaches the full state, after that it will start balancing. AGM first goes at full charge and nearing 90 % it will lower the charge in order to get to 100 %. So combining them on one charging spec is not going to work.

As others have stated, LiFePO4 and AGM do not have the same charging specifics, so cannot combine them. Lithium can be charged at full charge until it reaches the full state, after that it will start balancing. AGM first goes at full charge and nearing 90 % it will lower the charge in order to get to 100 %. So combining them on one charging spec is not going to work.

Since the bulk and float voltage of both AGM and LFP can be the same, the only difference between the two in terms of charging is absorption duration. AGM's acceptance rate is why people switch to lithium, but the short absorption duration of LFP doesn't matter since a smart regulator won't kick into Absorption until the target bulk voltage is reached and at that point the AGM is essentially full, assuming bulk is set to 14.4 vdc or thereabouts. As noted, my many years of charging LA and LFP with exactly the same charging sources would seem to suggest you may be missing something.

 

[Delfin]

In my opinion it should not be a problem to use a lithium battery bank for starting the engines, it is indeed only a short burst.
Linking start batteries and Lithium and then charging them at the same time..........that is something I would not do. Better to connect a separate charger, connect that to the lithiums and then start charging the start batteries. That way you will be safe.

Whether engine starting is a problem for LFP is solely a function of the BMS and internal wiring of the battery. Some can't handle the current required to turn the diesel, some can, like mine. So yes, you can, or no you can't. Opinions don't actually enter into the physics of the situation.